Disease-free Caucasians with a haplotype containing the HLA Class II alloantigens DR2 and DR3, -- the same Class II alloantigens which are associated with systemic lupus erythematosus (SLE), -- are more likely to have impaired Fc- mediated mononuclear phagocyte system clearance than individuals without these alloantigens. This same difference is reflected in the specific impairment of Fc receptor-mediated phagocytosis by blood monocytes in the same groups. We hypothesize that different Fc receptor forms and allelic variants, which have important functional consequences for the host, underlie these findings. Accordingly, the specific aims of this proposal are: 1. to define the different biochemical forms of Fc- gamma receptor and establish the presence or absence of a comma polypeptide core; 2. to define the different epitopes on these FcRs by monoclonal and polyclonal antibodies; 3. in populations defined by DR type and intrinsic phagocytic capacity as we have described, to define the expression of different receptors and/or allelic forms using a) receptor isolation and analytic isoelectric focusing and b) fluorescent analysis with monoclonal anti-receptor antibodies; 4. using receptor-specific reagents, to define the consequences of ligation specific different FcR forms in terms of a) transmembrane signalling events (e.g., intracellular calcium measured by Indo I) and b) receptor initiated integrated cell functions (e.g., E- ConA phagocytosis in NA1 and NA2 homozygotes). Phagocytosis by blood monocytes of Fc specific and non-specific probes is assessed by radiometric incorporation; one- and two- dimensional SDS-PAGE and Western blotting of affinity-isolated Fc receptor are used to defined molecular weight, isoelectric points, lectin-binding and epitope representation. Electroelution and HPLC are used for protein purification for sequencing. Flow cytometry defines surface epitopes and changes in intracellular calcium (Indo 1). These studies will define the mechanism underlying HLA- associated differences in Fc receptor function and provide a basis for more guided therapeutic approaches in diseases such as SLE.